Add ArchUnit guards for Java multi-frontend boundaries in a test-only
module. Identify PBS by frontend-module origin, allow only the registry
as composition root, and lock the wording in specs 19, 20, and 22.
Housekeep DSC-0064 with LSN-0066.
Publish the language-versus-platform validation matrix in compiler-general
specs, retitle spec 19, and recut PBS diagnostics so common structural
failures are not PBS coverage.
Housekeep DSC-0060 with LSN-0063.
Move lifecycle assembly out of the PBS frontend into a common
AssembleLifecyclePipelineStage. PBS emits a typed IRLifecycleDeclaration;
the assembler owns wrappers, boot guard, and single project-init execution.
Housekeep DSC-0059 with LSN-0062, and include the DSC-0062 PVM/PBX
neutrality spec and lesson already present on this branch.
